Thanks for all the help.
In the end, one of the MinGW users on their mailing list (Eli Zaretskii) pointed me in the right direction.
fmt.exe now lives here in Sourceforge:
It needs two DLL libraries (libintl and libiconv) which get copied across into the git bash bin directory too. They live here in Sourceforge:
libintl
libiconv
Now, this little lot will get fmt.exe working in your git bash, but lsvirtualenv still does not work properly... but I think that is a virtualenvwrapper problem now!